Reversible focal hyperthermic effects on evoked auditory cerebral responses

The click-induced cerebral response recorded as three positive and three negative waves (P 1, P 2, P 3, and N 1, N 2, N 3) from the auditory receiving cortex of cat was selectively modified by focal hyperthermia (FBF). (a) In the posterior ectosylvian gyrus with FBF of 41°C, there was enhanced amplitude of P 2 (24 to 40 ms, latency) and N 2 (44 to 62 ms) waves compared with responses recorded from cortex prior to treatment. (b) Similar enhancement occurred in the middle ectosylvian gyrus with FBF but the effect on the N 2 wave was less prominent. (c) In the anterior ectosylvian gyrus, the amplitude of the N 2 wave was enhanced to a greater extent than the P 2 wave by FBF. (d) In gyrus ansatus, adjacent to the anterior ectosylvian gyrus, FBF resulted in enhancement of the N 1 (16 to 22 ms) wave with smaller increases in the P 2 wave. P 3 N 3 waves showed increased amplitudes but with less stability than those described above. These observations indicate that focally elevated temperatures of auditory receiving cortex result in increased activities which can be recorded as selective enhancement of components of the click-evoked response. Compatible observations, obtained during FBF of the cerebellar auditory receiving area, show increased amplitudes and frequencies of efferent discharges in the superior cerebellar penduncle.